1. Field of the Invention
The present invention relates to a method of manufacturing a photomask including an absorber pattern on a reflective layer and, more particularly, to a method of manufacturing a photomask in a part of which the reflection coefficient of the absorber layer is changed. The present invention also relates to a semiconductor device manufacturing method using a photomask manufactured by this method.
2. Description of the Background Art
Along with the recent advance in the micropatterning of semiconductor devices, a demand for patterning with an EUV (Extreme Ultra Violet) lithography process has been increasing. The design rule of leading-edge devices has already reduced the half pitch (hp) to around 32 nm. An exposure technique using the EUV lithography process manages to cope with this micropatterning.
In the EUV lithography process a reflective mask has been used, the reflective mask having a multi-layered reflective layer comprised of silicon film and molybdenum film formed on a substrate and an absorber pattern comprised mainly of Tantalum formed on the reflective layer. Under these circumstances, the pattern dimensional uniformity required for the reflective mask is increasingly becoming stricter. To correct mask pattern dimensions of a transparent mask, a technique of changing the transmittance of a quartz substrate is available. This technique decreases the transmittance of quartz at a relatively large opening of the mask pattern within the mask plane (e.g., see A2 in PCT [WO] 2005/008333).
However, using this technique, the transmittance of the transparent mask may be changed, while the reflection coefficient of the reflective mask cannot be sufficiently changed. Moreover, this approach adjusts the amount of the transmittance change of the quartz substrate with a certain rule based only on a dimensional difference between the pattern actually formed on the substrate and the design pattern corresponding to the pattern. As a result, the pattern dimensions of the reflective mask cannot be corrected accurately and an appropriate amount of pattern correction suited to the mask pattern dimensions cannot be obtained.